dig segfaults when using +trace and the dns server of the domain is down

How-To-Repeat: Note: /usr/obj/usr/src/usr.bin/dig/dig is dig compiled with -ggdb

% /usr/obj/usr/src/usr.bin/dig/dig +trace optimuss.net 

; <<>> DiG 9.6.2-P2 <<>> +trace optimuss.net
;; global options: +cmd
.                       271909  IN      NS      l.root-servers.net.
.                       271909  IN      NS      k.root-servers.net.
.                       271909  IN      NS      i.root-servers.net.
.                       271909  IN      NS      f.root-servers.net.
.                       271909  IN      NS      m.root-servers.net.
.                       271909  IN      NS      e.root-servers.net.
.                       271909  IN      NS      h.root-servers.net.
.                       271909  IN      NS      c.root-servers.net.
.                       271909  IN      NS      d.root-servers.net.
.                       271909  IN      NS      j.root-servers.net.
.                       271909  IN      NS      g.root-servers.net.
.                       271909  IN      NS      b.root-servers.net.
.                       271909  IN      NS      a.root-servers.net.
;; Received 500 bytes from 139.18.25.3#53(139.18.25.3) in 1 ms

net.                    172800  IN      NS      c.gtld-servers.net.
net.                    172800  IN      NS      j.gtld-servers.net.
net.                    172800  IN      NS      g.gtld-servers.net.
net.                    172800  IN      NS      i.gtld-servers.net.
net.                    172800  IN      NS      d.gtld-servers.net.
net.                    172800  IN      NS      l.gtld-servers.net.
net.                    172800  IN      NS      e.gtld-servers.net.
net.                    172800  IN      NS      m.gtld-servers.net.
net.                    172800  IN      NS      f.gtld-servers.net.
net.                    172800  IN      NS      a.gtld-servers.net.
net.                    172800  IN      NS      k.gtld-servers.net.
net.                    172800  IN      NS      b.gtld-servers.net.
net.                    172800  IN      NS      h.gtld-servers.net.
;; Received 487 bytes from 202.12.27.33#53(m.root-servers.net) in 25 ms

optimuss.net.           172800  IN      NS      ns1.optimuss.net.
;; Received 64 bytes from 192.12.94.30#53(e.gtld-servers.net) in 58 ms

zsh: segmentation fault (core dumped)  /usr/obj/usr/src/usr.bin/dig/dig +trace optimuss.net


Here is the debug output from gdb

% gdb /usr/obj/usr/src/usr.bin/dig/dig dig.core 
GNU gdb 6.1.1 [FreeBSD]
Copyright 2004 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i386-marcel-freebsd"...
Core was generated by `dig'.
Program terminated with signal 11, Segmentation fault.
Reading symbols from /lib/libcrypto.so.6...done.
Loaded symbols for /lib/libcrypto.so.6
Reading symbols from /lib/libthr.so.3...done.
Loaded symbols for /lib/libthr.so.3
Reading symbols from /lib/libc.so.7...done.
Loaded symbols for /lib/libc.so.7
Reading symbols from /libexec/ld-elf.so.1...done.
Loaded symbols for /libexec/ld-elf.so.1
#0  0x080557cf in send_done (_task=0x28514000, event=0x285200e8)
    at /usr/src/usr.bin/dig/../../contrib/bind9/bin/dig/dighost.c:2128
2128                    ISC_LIST_DEQUEUE(sevent->bufferlist, b, link);
[New Thread 28563d80 (LWP 100221)]
[New Thread 28563ec0 (LWP 100220)]
[New Thread 28564140 (LWP 100149)]
[New Thread 28501140 (LWP 100187)]
(gdb) bt
#0  0x080557cf in send_done (_task=0x28514000, event=0x285200e8)
    at /usr/src/usr.bin/dig/../../contrib/bind9/bin/dig/dighost.c:2128
#1  0x08173f49 in run ()
#2  0x28354619 in pthread_getprio () from /lib/libthr.so.3
#3  0x00000000 in ?? ()